In a multiple access wireless communication system, it is highly desirable to maximize system capacity, providing a maximal or optimal level of service to a plurality of mobile stations (also referred to as subscriber units). To ensure a high quality of such service while maintaining system capacity at an optimal level, the transmit power of each mobile station is controlled through messaging from a base transceiver station (“BTS”) (also referred to as a base station). Preferably, the BTS issues control messages which provide that each mobile station is transmitting (on the reverse or “up” link) with only a power level necessary to maintain a predetermined link quality and to avoid unduly interfering with other transmitting mobile stations.
In multiple access wireless communication systems, such as code division multiple access (“CDMA”) systems, a signal from a mobile station is typically deteriorated by interference from noise in the environment, including signals from other mobile stations. This aggregate noise and interference by other mobile stations may be referred to as the “noise floor” of the communication system. In a CDMA system, with the coding gain provided by signal spreading with a pseudorandom sequence, a BTS may receive a signal transmitted from a mobile station at a prescribed quality level, even though that signal has a power level which is lower than the power of the noise floor. To maintain signal quality, however, the transmit power of a mobile station should not be lower than a predetermined threshold below the noise floor occurring within the system, during any given period of time.
The noise floor within the communication system may be changing, during any period of time, for example, as mobile units become active or inactive. In addition, recent proposals in CDMA communication systems include providing for a mobile station or other subscriber unit to transmit packets of data, at a comparatively high rate. To achieve such desired and comparatively high data rates, however, the transmitted power should be relatively large for packet data transmission compared to the lower data rates used for voice transmission, to enable data transmission with sufficient energy per data bit for maintenance of an acceptable link quality. Because CDMA systems preferably operate with a relatively stable noise floor, and because high speed data transmissions are typically bursty in nature, a sudden onset of a high power, high data rate transmission in a CDMA system may interfere with and cause frame errors and erasures in signals received from lower power, lower data rate transmissions from other mobile stations. Such interference may be noticeable, for example, as perceived by a listener in a voice communication, and generally may be unacceptable as a potential source of subscriber or consumer dissatisfaction.
Other examples of multiple access wireless communication systems exhibiting this characteristic behavior include multiple access Orthogonal Frequency Domain Multiplexing (“OFDM”) wireless communication systems and UMTS/WCDMA communication systems.
As a consequence, a need exists for a method and system to control reverse link transmission power of mobile stations in a multiple access system, to enable high power, high data rate transmission, while simultaneously providing acceptable, comparatively high communication link quality for lower data rate transmissions, such as for voice transmission.